Structuring database object with mongodb-native bindings for node.js

Question

I'm working on creating an object that I can reuse throughout my server. However, with the following example, I get, what appears to be two calls to 'create'. Any ideas why? Can I structure this better.

var mongo = require('mongodb');
var Server = mongo.Server;
var Db = mongo.Db;
var server = new Server('localhost', 27017, {auto_reconnect: true});

var Database = function(name) {
  this.db = new Db(name, server);
};

Database.prototype.create = function(collection, document, callback) { var db = this.db;

  db.open(function(error, db) {
    if (!error) {
      db.createCollection(collection, function(error, collection) {
        collection.insert(document, {safe: true}, function(error, result) {
          if (error) return callback(error, null);
          return callback(null, result);
        });
      });
    }
    return callback(error, null);
  }); 
};

var data = new Database('foo');
data.create('testing', {'foo': 'bar'}, function(err, result) {
  console.log(result);
});

Running the file results in:

kenneth@apollo:~/Projects/dwibbles$ node db.js 
null
[ { foo: 'bar', _id: 506ba4b0e3441ab82a000001 } ]

Why is this being called twice?

console.log(result);

UPDATE: It was pointed out that I had an incorrect conditional.

if (!error) {
  db.createCollection(collection, function(error, collection) {
    collection.insert(document, {safe: true}, function(error, result) {
      if (error) return callback(error, null);
      return callback(null, result);
    });
  });
} else {
  return callback(error, null);
}

Answer 1

Your callback is actually being called twice:

  db.open(function(error, db) {
    if (!error) {
      db.createCollection(collection, function(error, collection) {
        collection.insert(document, {safe: true}, function(error, result) {
          if (error) return callback(error, null);
          return callback(null, result); <-- this one gets called on collection insert
        });
      });
    }
    return callback(error, null); <-- this one gets called immediately after db open
  });

You probably meant something like this:

  db.open(function(error, db) {
    if (error) {
        return callback(error);
    }

    db.createCollection(collection, function(error, collection) {
      collection.insert(document, {safe: true}, function(error, result) {
        if (error) return callback(error, null);
        return callback(null, result); <-- this one gets called on collection insert
      });
    });

  });

Answer 2

See reason in the comment below:

Database.prototype.create = function(collection, document, callback) { 
  var db = this.db;
  db.open(function(error, db) {
    if (!error) {
      db.createCollection(collection, function(error, collection) {
        collection.insert(document, {safe: true}, function(error, result) {
          if (error) return callback(error, null);
          return callback(null, result);
        });
      });
    }
    return callback(error, null); // This line gets executed in the !error case too
  }); 
};

To fix:

Database.prototype.create = function(collection, document, callback) { 
  var db = this.db;
  db.open(function(error, db) {
    if (!error) {
      db.createCollection(collection, function(error, collection) {
        collection.insert(document, {safe: true}, function(error, result) {
          if (error) return callback(error, null);
          return callback(null, result);
        });
      });
    } else {
      return callback(error, null);
    }
  }); 
};